Case Klett

Case Klett

The commute for about 30 000 locals out of Trondheim on Fridays will no longer be a nightmarish activity, as a new four-lane stretch of the E6-highway will significantly enhance the traffic flow by spring 2019.

The commute for about 30 000 locals out of Trondheim on Fridays will no longer be a nightmarish activity, as a new four-lane stretch of the E6-highway will significantly enhanced the traffic flow by spring 2019. Totalling 8-km and going through exceptionally challenging topography in densely populated areas, the road project is an engineering nut to crack. Innovative technologies utilised for the construction looks to ensure project completion within budget and time.

The construction project got a green light in the Norwegian National Transport Plan 2014-2023, where politicians earmark funding to infra projects. PEAB delivered the most valued offer for the Aas-Jakobsen designed project and the project kicked off early 2016. The stretch of road will run through one of Norway’s largest areas of highly sensitive clays, which necessitates the use of a robust monitoring programme, as well as extensive stabilisation and mass-shift efforts.

Large scale quick clay stabilisation

The first and perhaps the most critical step in the project is ground condition stabilisation. Quick clay is a type of sensitive clay that is frequently found in Sweden, Norway, Finland, Russia and Canada due to the ice age. It is characterised by its liquid structure, which, if distressed by human activity or erosion, can collapse. This leads to so-called quick clay slides in which many lives and properties have perished throughout the years. For this project to even be feasible, lime-cement stabilisation on a grand scale had to be set into motion with the help of The Norwegian Geotechnical institute. “We’ve drilled more than 44 000 boreholes and filled them with 50/50 lime and cement to ensure the masses are stable and resistant to external pressure. Due to excavation and the depth of the clay deposits, each hole is 25 m deep and has a diameter of 600 mm. So quite a unique large-scale stabilisation effort,” says Geotechnical Engineer Lars Andreas Solåsfrom Norwegian Public Roads Administration. In addition to lime cement stabilisation, the project called for moving of more than 2M cubic meters of masses, of which 500 000 cubic meters were moorland properties. Quality clay was shifted and will be re-used for another stretch of the road but then laid out in thin layers and compressed to ensure stability.

Automated monitoring

Before mass-shifting began, the project team decided to follow-up the pre-filling of one of the embankment of the road project using automatic intelligent devices to monitor and understand the settlement. The choice of methodology landed on FinMeas’ liquid-filled settlement hose. The tool works so that pressure cells are placed at given intervals, and they measure settlement down to 5 mm. Signals are transferred from the pressure cells via a control unit to an online system which is equipped with graphs and deformation limits and alarm in case they are exceeded. “The settlement system has given the project team a unique chance to post-calculate the settlement curve from the prefill, and to understand the settlements taking place after prefilling removed” states Geotechnical Engineer Stian Berre from Multiconsult. Other deliveries from FinMeas to the project include four inclinometers, which are used to measure the displacement of retaining walls. The 40-m deep inclinometers are situated close to the large excavation in quick clay to monitor if there are any movements and possible landslides. The data from all FinMeas' monitoring equipment is logged continuously to FinMeas Online, through which the PEAB project team can easily monitor the conditions on the construction site at all times. The alarm-equipped system saves the project team not only time and money, but also gives them a chance to act early should anything go wrong. The new stretch of the E6 is scheduled to be completed by spring 2019.

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